Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders having a read head and a write head. An actuator/suspension arm holds the slider above the surface of a magnetic disk. When the disk rotates, an air flow generated by the rotation of the disk causes an air bearing surface (ABS) side of the slider to fly to a particular height above the disk. As the slider flies on the air bearing, a voice coil motor (VCM) moves the actuator/suspension arm to position the read/write head over selected tracks of the disk. The read/write head may then read data from or write data to the tracks of the disk.
A conventional disk includes data fields where the actual data is stored. In the data fields, the magnetic surface of the disk is divided into small magnetic regions, each of which is used to encode a single binary bit of information. The magnetic regions include a few dozen magnetic grains forming a magnetic dipole, which generates a highly localized magnetic field. The write head magnetizes a magnetic region by generating a strong local magnetic field to store a bit of data within the magnetic region during a write process. The read head senses the magnetic dipole of the magnetic region to read the bit of data during a read process.
As the areal bit density of the disk increases, the magnetic regions encoding the bit data become smaller. This may reduce the read signal generated in the read head. One solution to improve the read signal is to reduce the thickness of the carbon overcoat that is typically applied to the disk for protection. The carbon overcoat is a non-magnetic layer applied to the magnetic films used store the bit data on the disk. Thus, reducing the overcoat thickness potentially reduces the relative distance between the ABS side of the slider and the magnetic films, which improves the read signal generated in the read head. However, as the overcoat becomes thinner, the corrosion resistance of the disk may degrade, especially if the overcoat is rough.
Another solution to improving the read signal is to reduce the clearance between the ABS side of the slider and the top surface of the disk. However, one consequence of a reduced clearance between the slider and the top surface of the disk is head-to-disk contact, which is undesirable. Head-to-disk contact occurs when the ABS side of the slider makes contact with the disk. Head-to-disk contact may cause damage to the slider, the disk, or both. It therefore remains an ongoing challenge to increase the areal bit density on the disk to improve the storage capacity of disk drive systems.